1. Field of the Invention
The present invention relates, in general, to monitoring proper operation of a latching or locking mechanism such as ratchet and pawl, and, more particularly, to systems and methods for sensing proper operation of a pawl and ratchet assembly including detecting proper insertion or travel of a pawl into a valley between teeth of the ratchet such that the pawl blocks movement of the ratchet in a particular direction (e.g., allows forward motion but limits reverse motion). For example, a passenger restraint mechanism or a safety restraint may include a pawl and ratchet assembly according to the invention that provides monitoring of proper locking or latching of the restraint.
2. Relevant Background
Amusement parks continue to be popular worldwide with hundreds of millions of people visiting the parks each year. Park operators seek new designs for extreme or thrill rides that attract people to their parks, but safe operation of the new and existing rides is always a highest priority design requirement. For example, roller coasters and other thrill rides apply significant amounts of force (e.g., g-forces) on the passenger with numerous twists, turns, drops, and loops at speeds of up to 100 miles per hour or more. Ride designers or engineers are given the task of producing unique and more exciting rides that are safe and that are also less costly to operate and maintain.
Passenger restraints are one of the most important features in ride safety as these restraints comfortably and securely keep passengers in place in a seat or within a ride car or compartment. Ride engineers continue to evaluate new kinds of passenger restraint systems that meet safety requirements while being less expensive to operate and maintain. Maintenance of an amusement park ride including maintaining passenger restraints often is a tedious process including daily, monthly, and yearly inspections. Even the daily inspections may take hours to perform as an inspector not only verifies proper operation of the ride but at least periodically performs an extensive inspection of the ride track and other ride machinery including components of passenger restraint systems (e.g., inspect for unacceptable wear of parts especially load bearing parts and mating components, for proper operation of moving parts such as springs and for proper tightening of fasteners). To reduce the costs associated with maintenance, ride designers continue to look for ways to automate these inspections and otherwise simplify the inspectors' tasks.
During operation of a ride, a passenger restraint is typically placed across the lap or over the shoulder of a ride passenger, and a mechanism is typically provided as part of the restraint that locks or latches the restraint in place during operation of the ride. In some cases, ride designers are required to comply with governmental regulations or with standards that establish criteria for the design of amusement rides including criteria regarding passenger restraints. For example, many rides are designed to meet or exceed criteria provided in the ASTM F2291 standard, which is entitled “Standard Practice for Design of Amusement Rides and Devices.” With regard to passenger restraints, ASTM F2291 calls for rides that create accelerations that lift guests or passengers out of their seats (i.e., Class 5 restraints) to be designed such that failure of a restraint to properly operate prevents the next ride cycle from starting. Proper operation for passenger restraints includes the locking or latching mechanism properly engaging to prevent the restraint from opening during the ride cycle, and, hence, monitoring operation of a passenger restraint involves determining whether the locking or latching mechanism has engaged or is secured.
For some passenger restraint designs, sensors are used to identify whether the passenger restraints are properly secured. A direct sensor such as a proximity sensor (e.g., a Hall effect sensor), a displacement sensor, a pressure sensor, a force sensor, or the like may be used to determine when the mechanism is operating properly such as when a tongue latches inside a buckle, and the sensor transmits a signal to a controller or a restraint monitoring module running on a computer that acts to process sensor signals to monitor proper operation of all the restraints on a particular ride. If a sensor indicates that a restraint did not work correctly, the controller detects the problem and prevents the ride operating system from beginning the next ride cycle. For example, direct sensors (i.e., a sensor associated with each restraint that directly monitors engagement of the locking or latching mechanism components) are utilized with hydraulic passenger restraints to verify proper operation of the restraint. Use of hydraulic restraints in some implementations has created some operating issues. For example, their use may involve a ride operator having to tug or pull on each restraint after it is positioned over a passenger relatively hard to generate enough hydraulic pressure in the restraint structure such that the sensor signal indicates to the controller that the restraint is properly secured or engaged, and the repeated tugging or pulling motion can be physically demanding for some operators and generally delays the start of the next ride cycle while the operator checks each restraint. Such tugging or physical verification is present in other restraints that do not utilize hydraulics. With these issues in mind, ride designers continue to evaluate other mechanisms for securing or locking passenger restraints.
Ratchets are convenient devices for ride designers to use in passenger restraint assemblies because they rotate in one direction but not in the other when a pawl engages teeth of the ratchet or the ratchet wheel. For example, an over-the-shoulder restraint may include a pawl and ratchet assembly to provide the latching and locking mechanism for the restraint. During operation, the passenger pulls the restraint down, and, during this motion, a spring or other actuator urges the pawl into engagement with the teeth. As a result, the passenger moves the restraint and the ratchet in one direction (e.g., downward), but the passenger and ride forces cannot push or move the restraint and the ratchet in the other direction because the pawl engages the ratchet teeth to stop motion in this direction. Pawl and ratchet assemblies are also relatively inexpensive to manufacture and maintain, and these and other characteristics make ratchets attractive for use in restraints and similar applications.
Pawl and ratchet assemblies have been widely adopted in the past and continue to be popular for less demanding applications. However, recent regulations (e.g., the ASTM 2291 standard) have limited their use for demanding applications (e.g., for use as part of Class 5 restraints) because it is often difficult to monitor their proper operation. For example, it is difficult to provide sensors within a pawl and ratchet assembly to directly monitor engagement of the pawl with the ratchet teeth. This has made it impractical to use a computer-based system to automatically monitor ratchets provided in restraints for proper operation based on sensor signals, and, hence, pawl and ratchet assemblies have not been used in rides and other applications where guests or passengers may be lifted out of their seats due to accelerations and g-forces generated by the ride or application (e.g., systems where the restraints have to meet ASTM F2291 criteria on monitoring proper engagement or similar design requirements). To be confident that the restraint will adequately prevent reverse motion when needed, a ride designer needs a way to verify that the pawl can move freely, as it passes over the teeth in the forward motion of the ratchet, into the valley or recessed surface between two adjacent teeth of a ratchet to resist reverse motion if movement of the ratchet is attempted in this second or reverse motion. In other words, because ratchets do not lock, the designer needs another way to monitor that a pawl and ratchet assembly will work properly to enforce one-way motion before starting a ride using such assemblies in the passenger restraints. Additionally, for rides where the direction of the g-loading changes throughout the ride, the ride designer needs to be assured that the pawl remains pressed into the valley between the teeth regardless of the g-loading direction. In many cases, a spring or resilient member is used for biasing the pawl into engagement in a valley between adjacent teeth, and, during operation of the ride, it is desirable to monitor continued operation or failure of the spring such as to verify that the ratchet will continue to work for various g-loading directions.
One of the main reasons that it is difficult to provide a sensor for direct monitoring of operating status of a pawl and ratchet assembly is that actual pawl movement or travel at the point of engagement with the ratchet teeth (i.e., the ratchet engagement portion of the pawl) is relatively small. As a result, small variations in pawl travel that may be caused, for example, by debris or other mechanical problems are difficult to identify when compared with the normally narrow range of motion of the ratchet engagement portion of the pawl. To directly monitor the range of motion of the ratchet engagement portion of the pawl, it may be possible to mount a high precision sensor at or near the point of engagement, but this is often impractical due to small physical clearances for placing a sensor within the assembly and due to increased costs. Further, accurate monitoring requires that such sensors be precisely adjusted to achieve desirable results, which places additional burdens on the ride operators at initial installation and during ongoing maintenance as the sensors may need to be periodically calibrated and tested. Alternatively, it has been suggested that much larger ratchets may be used as part of restraints such that the ratchet engagement portion of the pawl has a longer travel path to be pressed into the valley between two ratchet teeth. Larger ratchets are also generally not practical in many applications as the ratchets cannot physically fit within the housing or other physical limitations of the ride design, and such ratchets often significantly increase the weight of the ride.
Passenger restraints of all kind may be designed to include pawl and ratchet assemblies and exemplary passenger restraints include over-the-shoulder restraints, shoulder or lap belts, bar, or other restraints for amusement park rides, automobiles, airplanes, trains, ski-chair lifts, and the like. Additionally, there are other applications where it is desirable to monitor proper operation of a locking or latching mechanism such as a pawl and ratchet assembly. For example, the shipping industry utilizes tie downs to secure cargo during transport by ship, train, truck, airplane, or the like, and the tie downs are secured to avoid excessive movement of the cargo when forces are applied. In these cases, pawl and ratchet assemblies may be utilized, and an operator needs to verify proper engagement and operability of any biasing components. As another example, in factory environments, pawl and ratchet assemblies may be used to limit conveyor belt or other moving part motion to a single direction, e.g., a conveyor belt cannot roll backwards. In these settings, as with passenger restraints, it may be difficult to use sensors to directly monitor proper engagement or operation of the assemblies. Ratchets are also used in business machines such as copiers and printers, and, while safety often is not an issue, it is desirable to monitor continued proper operation of pawl and ratchet assemblies to quantify use and provide diagnostic monitoring of the machines and direct monitoring of small pawl movements is challenging.